The present invention relates to the treatment of subterranean formations. More particularly, the present invention relates to methods for stabilizing portions of a subterranean formation and controlling the production of water from those subterranean formations.
Hydrocarbon wells are often located in subterranean formations that contain unconsolidated particulates (e.g., sand, gravel, proppant, fines, etc.) that may migrate out of the subterranean formation with the oil, gas, water, and/or other fluids produced by the wells. The presence of such particulates in produced fluids is undesirable in that the particulates may abrade pumping and other producing equipment and/or reduce the production of desired fluids from the well. Moreover, particulates that have migrated into a well bore (e.g., inside the casing and/or perforations in a cased hole), among other things, may clog portions of the well bore, hindering the production of desired fluids from the well. The term “unconsolidated particulates,” and derivatives thereof, is defined herein to include loose particulates and particulates bonded with insufficient bond strength to withstand the forces created by the production of fluids through the formation. Unconsolidated particulates may comprise, among other things, sand, gravel, fines and/or proppant particulates in the subterranean formation, for example, proppant particulates placed in the subterranean formation in the course of a fracturing or gravel-packing operation. The terms “unconsolidated subterranean formations,” “unconsolidated portions of a subterranean formation,” and derivatives thereof are defined herein to include any formations that contain unconsolidated particulates, as that term is defined herein. “Unconsolidated subterranean formations,” and “unconsolidated portions of a subterranean formation,” as those terms are used herein, include subterranean fractures wherein unconsolidated particulates reside within the open space of the fracture (e.g., forming a proppant pack within the fracture).
One method of controlling particulates in such unconsolidated formations has been to produce fluids from the formations at low flow rates, so that the near well stability of sand bridges and the like may be substantially preserved. The collapse of such sand bridges, however, may nevertheless occur, possibly due to unintentionally high production rates and/or pressure cycling as may occur from repeated shut-ins and start ups of a well. The frequency of pressure cycling is critical to the longevity of the near well formation, especially during the depletion stage of the well when the pore pressure of the formation has already been significantly reduced.
Another method of controlling particulates in unconsolidated formations involves placing a filtration bed containing gravel (e.g., a “gravel pack”) near the well bore to present a physical barrier to the transport of unconsolidated formation fines with the production of desired fluids. Typically, such “gravel-packing operations” involve the pumping and placement of a quantity of certain particulates into the unconsolidated formation in an area adjacent to a well bore. One common type of gravel-packing operation involves placing a screen in the well bore and packing the surrounding annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The screen is generally a filter assembly used to retain the gravel placed during the gravel-pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of the gravel-pack sand used. Similarly, a wide range of sizes of gravel is available to suit the characteristics of the unconsolidated particulates in the subterranean formation. To install the gravel pack, the gravel is carried to the formation in the form of a slurry by mixing the gravel with a treatment fluid, which is usually viscosified. Once the gravel is placed in the well bore, the viscosity of the treatment fluid may be reduced, and it is returned to the surface. The resulting structure presents a barrier to migrating sand from the formation while still permitting fluid flow.
However, the use of such gravel-packing methods may be problematic. For example, gravel packs may be time consuming and expensive to install. Due to the time and expense needed, it is sometimes desirable to place a screen without the gravel. Even in circumstances in which it is practical to place a screen without gravel, it is often difficult to determine an appropriate screen size to use as formation sands tend to have a wide distribution of grain sizes. When small quantities of sand are allowed to flow through a screen, formation erosion becomes a significant concern. As a result, the placement of gravel as well as the screen is often necessary to assure that the formation sands are controlled. Expandable sand screens have been developed and implemented in recent years. As part of the installation, an expandable sand screen may be expanded against the well bore, cased hole, or open hole for sand control purposes without the need for gravel packing. However, expandable screens may still exhibit such problems as screen erosion and screen plugging.
Another method used to control particulates in unconsolidated formations involves consolidating unconsolidated particulates into stable, permeable masses by applying a consolidating agent (e.g., a resin or tackifying agent) to the subterranean formation. Such resin application may be problematic when, for example, an insufficient amount of spacer fluid is used between the application of the resin and the application of the external catalyst. The resin may come into contact with the external catalyst in the well bore itself rather than in the unconsolidated subterranean producing zone. When resin is contacted with an external catalyst, an exothermic reaction occurs that may result in rapid polymerization, potentially damaging the formation by plugging pore channels, halting pumping when the well bore is plugged with solid material, or resulting in a downhole explosion as a result of the heat of polymerization. Also, using these conventional processes to treat long intervals (e.g., over about 20 feet) of unconsolidated regions is not practical due to the difficulty in determining if the entire interval has been successfully treated with both the resin and the external catalyst. Further, conventional consolidation techniques have often resulted in limited or inadequate penetration distances of consolidating agent into formations.
Unconsolidated formation particulates also may migrate out of the formation when water is produced from the formation. This migration of formation particulates is due, in part, to the fact that most natural cementation between formation sand grains disintegrates when in contact with an aqueous moving phase. The production of water from a subterranean producing zone is disadvantageous, among other reasons, both because of this effect of mobilizing formation sands, and because water production constitutes a major expense in the recovery of hydrocarbons from subterranean formations, especially in light of the energy expended in producing, separating, and disposing of the water. In order to combat these problems of water production, treatment fluids comprising relative permeability modifiers may be pumped into the subterranean formation that, among other things, may block water from entering certain portions of the subterranean formation and/or reduce the water-wettability of certain portions of the subterranean formation. These treatments may, inter alia, reduce the amount of water produced out of the subterranean formation. However, the addition of a separate treatment for applying a relative permeability modifier to a subterranean formation may add cost and complexity to the operations in that formation.